1. Field of the Invention
The present invention relates to a semiconductor process, and more particularly, to a semiconductor process of using an etchant including H2O2 for etching a recess.
2. Description of the Prior Art
For decades, chip manufacturers have made metal-oxide-semiconductor (MOS) transistors faster by making them smaller. As the semiconductor processes advance to very deep sub micron era such as 65-nm node or beyond, how to increase the driving current for MOS transistors has become a critical issue.
In order to improve device performance, crystal strain technology has been developed. Crystal strain technology is becoming more and more attractive as a means for getting better performance in the field of CMOS transistor fabrication. Putting a strain on a semiconductor crystal alters the speed at which charges move through that crystal. Strain makes CMOS transistors work better by enabling electrical charges, such as electrons, to pass more easily through the silicon lattice of the gate channel.
FIGS. 1-2 are schematic, cross-sectional diagrams illustrating a semiconductor process applying epitaxy technology in accordance with prior art. As shown in FIG. 1, a fabrication process for a semiconductor structure 10 includes the steps of first providing a substrate 12 and forming a gate structure 14 on the substrate 12. The gate structure 14 has a gate dielectric layer 14a, a gate electrode 14b, a spacer 14c and a cap layer 14d. An implantation process is performed to form a source/drain region at both sides of the spacer 14c within a specific region 16. A dry etch process is performed to the specific region 16 to form a recess having a predetermined depth (as shown in FIG. 1). A wet etch process is performed to the specific region 16 by using ammonia water as an etchant to form a V-shaped recess, as shown in FIG. 2. An epitaxial process is performed to form an epitaxial layer filled within the recess (not shown in FIG. 2).
It is should be noted that a recess etched by ammonia water has a V-shaped profile and the V-shaped profile typically results in circuit leakages and diminishes the electrical quality of the semiconductor device. Moreover, as the dimension of semiconductor devices scales down as the industry develops, the aforementioned issue of the recess profile affecting electrical property of the product also worsens substantially.